The early school age period is a time of significant developmental change in both cognitive abilities and neural systems. Yet little is known about how, specifically, these developmental processes that occur concurrently are linked to each other, or about the nature of critical interactions of biological factors with childhood experiences and environments. The proposed project takes a critical first step in addressing this problem by examining, in unprecedented detail, the development of basic cognitive processes and of the neural systems that mediate them during the child's transition to formal schooling. The design is a longitudinal study of 100 typically- developing children inducted at age 6 and assessed with behavioral measures and MRI annually on 5 occasions. The behavioral measures to be collected, of language, visuospatial processing, working memory, and cognitive control, have exhibited high sensitivity to developmental change over this age range. MR imaging of the children will involve recently developed, improved methods for image acquisition and computational modeling of the results. Diffusion parameters from specific brain fiber tracts as well as regional measures of cortical surface area and thickness will be measured. The focus of the study is on differences in the rate of fiber tract development from 6 to 10 years of age and links between this variability and the pace of cognitive development. Relationships between the neural parameters and early academic achievement will also be examined. The study is novel, not only because the imaging methods to be applied will produce more detailed information about the brains of children than is currently available, but also because of the conceptual focus of the project on the degree of concordance between trajectories of brain and behavioral development. The long-term significance of the study lies in its potential to guide us toward interventions that are more adaptive to individual differences and therefore promote positive outcomes in more children.